Furnace for the production of refractories



Feb. 18, 1964 E. H. AMSTEIN 3,121,617

FURNACE FOR THE PRODUCTION OF REFRACTORIES Filed April 20, 1961 Z SheetS-Sheet 1 RUTILE COKE MILLING MIXING MOLASSES EXTRUSION DRYING I?OC.

CALCI NI N6 IOOOC.

REACTION CARBON 22ooc. MONOXIDE 1 1641. RAPID COOLING TITANIUM CARBIDE Feb. 18, 1964 E- H. AMSTEIN 3,121,617

FURNACE FOR THE PRODUCTION OF REFRACTORIES Filed April 20, 1961 2 Sheets-Sheet 2 United States Patent 3,121,617 FURNACE FOR THE PRODUCTION OF REFRACTORIES Edmund Hollis Amsteiu, Chester, England, assign'or to The British Aluminium Company Limited, London,

England, a company of Great Britain Filed Apr. 20, 1961, Ser. No. 104,351 3 Claims. (Cl. 23-477) This invention relates to the production of refractory carbides, borides, boro-carbides and mixtures of refractory borides and carbides (all being compounds of the transition elements, titanium, zirconium, niobium and tantalum) or of boron carbide itself. The most important of these refractory compounds, at the present day, is titanium carbide and the following description will be directed mainly to the features and details of this invention as they apply to the production of this compound, although it is to be understood that such features and details, with appropriate modification as hereinafter indicated, are also applicable to the production of the other compounds listed above and that the present invention is accordingly not restricted to the specific examples given below.

This is a continuation-in-part of my copending application Serial No. 491,912, filed March 3, 1955, entitled: Production of Refractory Carbides, Borides, and the Like.

For economic reasons the reaction almost universally used for the production of titanium carbide on a commercial scale is the reduction of the dioxide TiO with carbon, according to the equation:

TiO +3 CQTiC-{JCO (i) The process is normally carried out at temperatures between 2000 and 3000 C. with the adoption of some precautions designed to avoid the occurrence of the backreaction which would give rise to the presence of oxygen and free carbon in the product. For instance, the reaction has been carried out under reduced pressure or in a vacuum, or the reaction has been carried out in a container which was sealed after reaction was complete, or the reaction has been carried out in a protective atmosphere, such as hydrogen. In spite of these precautions, however, it is extremely difiicult to obtain a commercial product containing more than about 92.5% of titanium carbide (i.e., about 18.55% combined carbon) or less than about 1% of free carbon. 7

The present invention has for its main object to provide an improved and economical process and an apparatus for its performance which, while utilizing Reaction i, will yield a product containing less free carbon than is usual in current commercial products, and if desired, a higher titanium carbide content and lower nitrogen content. A low free carbon content is very desirable in almost every application of titanium carbide, e.g., in hard metals, in cermets, and as cathodes or current leads in electrolytic cells for the production of refining of alu minum.

According to this invention, a process for the production of titanium carbide according to Reaction i which involves heating the reaction mass to a selected temperature in the range 2000 to 3000 C., is characterized by the step of rapidly cooling the mass as soon as possible after it has reached equilibrium at the selected temperature.

It has been found that the reaction rates are such that this rapid cooling will virtually eliminate back-reaction.

Preferably, the process is operated as a continuous one, the reaction mass or charge being passed at an appropriate speed successively through a zone of high temperature (e.g., 20002500 C.) and a zone of low temperature (e.g., a water-cooled zone). Under these conditions a good quality product is obtained without the trouble and expense of furnaces operating under vacuum or with a controlled atmosphere and at the same time all the commercial and economic advantages of a continuous process may be secured. I

The purity of the product obtained may also be greatly improved by reducing nitride formation, and by making use of a suitably selected binder in preparing the charge of titanium oxide and carbon, the binder containing constituents which have purifying and possibly catalytic properties.

The process according to the invention may be carried out by advancing the charge through a suitable furnace followed by a chilling zone while contained in boats or saggers made of some refractory materials such as graphite. However, not only do the saggers reduce the output of a given size of furnace proportionately to the space occupied by them, but both the heating and the chilling operations are delayed and their loading and unloading entail added process costs and complications. It is preferred, therefore, to produce the'charge in the form of self-supporting cylinders (or other convenient shapes) which can be advanced (e.g., either positively or under the action of gravity) as such through a fairly close-fitting graphite tube which is disposed more or less horizontally and is heated by passage of electric current through a graphite resistance element. The exit end of the tube is connected directly to a Water-cooled copper quench tube into which the cylinders or the like pass while still at a high temperature. In this way a large output can be obtained from a relatively small, and therefore economical, furnace. It should be noted that the heated zone of the furnace tube is preferably surrounded by heatinsulating material such as carbon black.

Certain requirements must be fulfilled in regard to the gas outlet from this furnace. The charge in passing through the furnace loses about half its weight in the form of carbon monoxide and at temperatures between about 500 and 1000 C. This gas can decompose according to the equation:

2co2c0,+c

If, therefore, the carbon monoxide formed in the reaction were to be allowed to escape at the ends of the furnace tube it would deposit carbon both on the charge entering the furnace and on the finished carbide leaving the furnace. Both these deposits would lead to an increase in the amount of free carbon in the product. It has been found that this effect can be eliminated by sealing the ends of the furnace and providing a gas outlet near the high temperature zone of the furnace. For example, the inlet or charging end of the furnace may be fitted with a gas-tight diaphragm which will permit the passage of the charge and the delivery end of the quench tube may open into a gas-tight chamber in which the product is collected. The gas outlet may open into the furnace tube at a zone where the temperature is above approximately 1500 C. and preferably about 2000" C. A further advantage of this arrangement is that any volatile impurities evolved at these high temperatures are carried out of the furnace in the high temperature gas stream and do not give rise to difficulties by condensing in the cooler inlet and outlet sections of the furnace. The carbon monoxide evolved can be disposed of by being burnt at the gas outlet, or it may be removed and stored for use as a fuel gas.

In order that the reactions may be carried out in this way, certain precautions must be taken when preparing the cylinders (or other bodies) which compose the charge. Thus in spite of the fact that these cylinders are to be quickly heated up to 2000 C. or more and then rapidly example, ball mills.

L3 cooled, losing half their weight in the process, they must not at any time change their shape, break, or disintegrate, in such a manner as to make it difficult to maintain the smooth passage of the charge through the furnace. The preparation of a satisfactory charge depends largely on the binder used and on the particle size of the constituents.

In the production of titanium carbide according to this invention the preferred raw materials are a pure grade of mineral rutile, a pure coke, and a carbonaceous binder. Current commercial practice usually requires the use of a pure precipitated titanium dioxide and carbon black, With or Without a binder. These materials can also be used in the present process but the preferred raw materials are much cheaper and the process makes it possible, nevertheless, to obtain a product which has a lower free carbon content than, and contains as much combined carbon as, the commercial product available at the present time.

The first step in the preparation of the charge is to grind the appropriate quantities of carbon (in the form of coke) and rutile, either together or separately, in for When steel balls are used iron contamination of the product may be considerably reduced by lining the mill with rubber. Iron contamination may be still further reduced by using a rubber-lined mill and carbide balls. The finer the particles of the charge, the stronger will be the cylinders or other shaped elements produced therefrom, both during and after the reaction. A strong cylinder is desirable as being unlikely to break in the furnace but, on the other hand, a friable productis desirable when it is to be crushed and ground to produce a carbide powder suitable for any sintering process, including hot pressing, in the manufacture of hard metals, etc. It is possible, by suitably controlling the grinding of the raw materials, to produce carbide cylinders of about optimum strength, i.e., strong enough to feed statisfactorily through the furnace but at the same time sufiiciently friable to grind down easily.

The next step is to agglomerate the ground raw material with the aid of a suitable binder, for example, pitch or cane sugar molasses. In the case of pitch, the appropriate quantity (generally 20-25%) is added as a coarse powder to the partly ground rutile-coke mixture in the ball mill, and milling is then continued for about 2 7 hours. The resultant powder can be extruded, to give the desired cylindrical {form of charge, provided it is heated to about 20 0'" C. The extruded rod is broken up into appropriate lengths and is now in its final form, except that the volatiles in the pitch ,must be removed by heating to about 1000 C. in a non-oxidizing atmosphere. This can be done in any convenient type of muffie furnace, and the resulting charge fulfills all the requirements of the high temperature furnace for producing the carbide.

The principal difiiculty in this step of the process when pitch is used lies in the calcination stage (heating to 1000 C.). If the batch size is large, volatiles from the outer hot zones condense in the center and cooler portion of the batch during heating. This condensate destroys the shape of the cylinders and renders the center of the batch useless. This difliculty becomes more serious as the scale of the process increases.

It is preferred, therefore, to employ cane sugar molasses as the binder because this is very satisfactory and is found to have quite unexpected effects on the purity of the product. In using this binder, an appropriate quantity (generally 2.045%) is mixed With the ground ruti-le and coke in a suitable mixer, such as one having sigma blades, and the product is extruded cold. It is dried in an air oven (at say mil-110 C.) and then has an excellent green strength. It is then loaded directly, while still hot, into the calcination furnace. No difliculties are experienced due to condensation in the center of the charge when the temperature in the furnace is raised to about 1000 C. in about 6 hours. It is also possible when using the molasses binder, to calcine the cylinders, with or without pre-drying, in a continuous operation, the cylinders being passed down a heat-resisting tube which is fitted with gas outlets and is heated by gas or electricity so that in the course of the travel of a cylinder down the tube (during as short a time as 30 minutes) its temperature will be raised from room temperature to 1000" C.

The final step in the production of titanium carbide is to [feed the charge continuously, prepared as above, by Way of the air-tight diaphragm into the high temperature reaction furnace where it passes successively through the high temperature Zone and the zone of low temperature into a hermetically sealed receiver from which it can be removed as required. It is preferred to feed the charge to the furnace at a temperature of 50100 C. since it has been found that by so doing the corrosion due to water vapor on the [furnace tube is minimized. This is particularly necessary if the charge has been standing for a period at room temperature after the calcination step at 1000 C. since a small amount of Water vapor is adsorbed by the charge and subsequent heating to C. has beenfound to remove this Water vapor.

As already mentioned, the use of molasses as the binder also confers quite unexpected benefits in yielding a much purer product than do other binders. This increase in purity is thought to be due to some form of catalytic action exercised by the inorganic content of the molasses. An average molasses sample contains about 8% of inorganic material; the principal metallic constituents being potassium, sodium, calcium, iron, silicon, and magnesium, with chloride, phosphate, and sulphate as the acid radicles. These constituents are largely or entirely volatilized during passage through the high temperature furnace and it is quite possible that their catalytic activity is exerted in part in the vapor phase. The effect of these inorganic salts is all the more surprising in that Hilttig (Z. anorg. u. allgem. Chem, 1952 270, 33) has reported that the chlorides of's-ome of the alkali metals and alkaline earths do not have any beneficial effect on the reaction between TiO and carbon. It is possible, however, that this difference is due to the con tinuous nature of the process according to this invention, which enables these compounds, whether in the state of solid or vapor, to remain in contact with the charge at all stages of the reaction.

The enhanced purity of the titanium carbide product prepared from a charge bound With molasses is illustrated by the following figures:

it will be seen that the titanium carbide content is notably high and the free carbon content notably low. In addition, the iron content of the material is reduced as compared with the product from a pitch-bound charge using the same rutile, coke, and preparative procedure. The lowering of the iron content may be explained by assuming that some of it is lost as a volatile compound (formed from the inorganic components of the molasses.

Analyses of commercial samples of titanium carbide show the presence of combined nitrogen equivalent to as much as 4% TiN. This contamination is not always desirable and if its formation is not allowed for in making up the furnace charge, then free carbon equivalent to it will be found in the product. This nitrogen contamination can arise either from residual air in the furnace or from the charge itself. Nitrogen from the furnace can be minimized by having a reasonably gas-tight furnace container, and by sweeping it out with an inert gas, e.g., carbon dioxide, before heating the furnace. Nitrogen in the charge can be present as gas adsorbed on the fine powders used. In the process of this invention this gas is largely if not entirely removed during the preliminary calcination step. Some forms of carbon, e. g., coke, also contain small amounts of nitrogen which cannot be removed by heating to 1000" C. and which appear as nitride in the titanium carbide produced from them. The remedy here is to choose a coke with a low nitrogen content. By taking all appropriate precautions it has been found possible to reduce the nitride con-tent of the titanium carbide to as little as 0.5%, and a content as low as 1% is easily achieved.

When desired, a further control over the free carbon content of the product, whether produced with the aid of pitch or molasses as the binder, can be achieved by incorporating a small quantity, e.g., about 1%, of alumina into the charge prior to the heating thereof. The alumina can be conveniently incorporated during the milling of the constituents of the charge. Under the conditions obtaining in the process according to this invention, alumina reacts selectively with free carbon contained in the titanium carbide formed, but not with the titanium carbide, according to the equation:

It should be noted moreover, that the alumina does not appear to react with carbon in the charge during the process of carbide formation. It is thus possible to reduce materially the free carbon content of the product by adding to the charge an amount of alumina which is equivalent to the free carbon content that would otherwise be expected to appear in the product, i.e., in the absence of this alumina.

It should perhaps be emphasized that the relatively pure products described were obtained from the comparatively impure raw materialunrefined mineral rutile. It has been found, however, that the vanadium and zirconium which are present as impurities in the mineral rutile are not removed even when using molasses as a binder. The product from mineral rutile therefore contains about 0.5% of both vanadium and zirconium. If in any particular application the presence of these elements is harmful, they can be eliminated by the use of pure precipitated titanium dioxide in place of mineral iutile. In this case the titanium dioxide is mixed with ground coke in the mixer at the point in the process where the molasses is added. Thereafter the process is carried out as when using mineral ru tile. The combined carbon content of the product remains unaffected at about 19.2% carbon.

There is given below one practical example of the way in which this invention may be practiced in producing titanium carbide, reference being made to the accompanying drawings, wherein:

FIG. 1 is a flowsheet diagram showing the steps in the process,

FIG. 2 is a side view, partly in longitudinal section and with parts broken away, showing a high temperature furnace suitable for use in carrying out the process, and

FIG. 3 is a section taken on the line III-III of FIG. 2.

3620 g. of rutile and 11430 g. of coke (low in ash and nitrogen) are ball-milled together for hours in a 10 rubber-lined mill with a charge of /2" steel balls. The resultant powder is mixed with 1470 g. of cane molasses in a sigma-bladed mixer for 20 minutes and then extruded to give cylinders in diameter and about 1 /2" long. These cylinders are dried for 12-14 hours at a temperature of 100-110 C. and then fired during 6-7 hours up to about 1000 C. in a non-oxidizing atmosphere. After they have cooled, the cylinders are fed through a high temperature furnace of the character referred to above. The center tube of this furnace is in diameter and is heated electrically for about 12'' of its length by means of a graphite resistance element. Over this portion of the length of the furnace there is a temperature gradient rising from 1000 C. at the inlet end to 2200 C. at the end nearer the water-cooled quench section. The cylinders are fed through this furnace at a rate such that 10-00 g. (2.2 lbs.) of titanium carbide will be produced per hour. The furnace tube is lagged with carbon black and its power input is 8 lcw. The yield is quantitative (based on titanium) and the product contains 96.5% TiC, 0.3% free carbon, 2% TiN and 0.2% Fe.

It is also a feature of the present invention to employ the methods and apparatus described above in the preparation of the refractory carbides of the transitional elements such as Zr, Nb and Ta, from the oxides of these elements and carbon.

'In these cases, the grinding of the oxide and carbon, and the percentage of binder used in making the furnace charge, are modified as required to yield a material that can be satisfactorily extruded or otherwise compacted, calcined, and fed through the high temperature furnace, and both the higher temperature and the temperature gradient within this furnace, and the time of passage of the charge through the hot zone of the furnace, are suitably chosen to yield a product of optimum purity. The time of passage of the charge through the hot zone of the furnace may be modified, within limits, by changing the linear rate of passage of the charge through the furnace and by changing the length of the hot zone of the furnace.

The methods and apparatus described above may also, as another feature of this invention, be employed in the preparation of the refractory borides and bore-carbides, and in the preparation of mixtures of the refractory borides and carbides, of titanium and the transitional elements listed above, using reactions of the type exempli tied in the following equation:

TiO +2C+2B=TiB +2CO (iii) and reactions of the type exemplified by Equation i, the composition of the product being predetermined by controlling the composition of the charge.

Again, as yet another feature of the invention, the methods and apparatus described above may also be employed in the preparation of refractory borides and borocarbides, and in the preparation of mixtures of the refractory borides and carbides, of titanium and the transitional elements listed above, using reactions of the type exemplified in the following equation:

and reactions of the type exemplified by Equation i, the composition of the product being predetermined by controlling the composition of the change. When utilizing reactions of type illustrated by Equation (iv), the use of these methods and apparatus ensures that the relatively volatile boric oxide is economically used whilst still maintaining the conditions of a continuous process and the rapid cooling of the product which inhibits backreaction with carbon monoxide.

It will be noted that in reactions of the type exemplified by Equation iv a considerable proportion of the weight of the reactants is lost as carbon monoxide. In consequence if pre-calcined cylinders are fed to the reaction furnace in the normal way they do not retain their shape during passage through the furnace, and at the same time suffer considerable disintegration. It is therefore preferred to use saggers or boats to contain the charge when using reactions of this type. A further difliculty of this type of Reaction iv lies in the volatility of the boric oxide, which has already been mentioned, which necessitates the use of quantities of the oxide in excess of the stoichiometric requirement, but still more economical use of boric oxide can be achieved by incorporating in the charge a quantity of an oxide which combines with or dissolves in the boric d oxide. Thus the incorporation of an amount of magnesia equal in Weight to the boric oxide results in a smooth reaction and a substantially complete conversion of the boric oxide to boride. When the final reaction tempera ture is in excess of 2000 C. the magnesia can be removed from the charge by incorporating an amount of carbon suflicient to react with the magnesia, according to the equation:

MgO+C=Mg+CO the magnesium being volatile at these temperatures.

When utilizing Reaction iii, Reaction iii combined with Reaction i, Reaction iv, or Reaction iv combined wth Reaction i, it is not possible invariably to prepare a boride entirely free from carbide even when this is desirable. Although the composition of the product can be to a large extent controlled by the composition of the charge, limitations are sometimes imposed by the relative stabili ties of the boride and carbide, and of the boro-carbide when it exists, of each particular transitional element. Preliminary experiments will, however, serve to establish both the limitations and the optimum conditions in each particular case where prior knowledge is in adequate. For example, 964 g. of rutile and 204 g. of coke are milled together for hours and then 381 g. of commercial boron of about 75% purity are added. The powders are then mixed with 580 g. of molasses and the mixture extruded, dried and calcined as described in the previous example. After cooling the cylinders are fed through the high temperature furnace at a rate such that 500 g. of titanium boride will be produced per hour. The power input of the reaction furnace is adjusted to give a maximum temperature of about 2206 C. The product has the follow ing composition: 95% TiB 2.0% TiC, 0.5% free carbon, 0.5% Fe.

According to another feature of this invention, the methods and apparatus described above may also be em ployed with advantage in the preparation of boron carbide using the reaction of the following equation:

FIG. 1 is a flowsheet diagram showing the steps in a typical production of titanium carbide by the process of this invention, starting from the raw materials rutile and coke and employing molasses as the binder. The steps of milling, mixing, extrusion, drying and calcining are all carried out with the aid of known apparatuses for these purposes. A suitable high temperature furnace equipped with means for rapidly cooling the solid product of the reaction effected therein is illustrated in FIGS. 2 and 3.

In these figures, the calcined cylinders composed of a mixture of ground rutile and coke are indicated by the reference numeral 1 and the cylinders of titanium carbide produced are indicated by the reference numeral 1a.

The apparatus for the production of refractory carbides, borides and the like according to the invention comprises generally a furnace insulated from and disposed within an outer casing. The furnace includes a substantially horizontal graphite tube supported from end walls of the casing and disposed axially within a graphite resistance element in the form of a longitudinally slit elongated tube, a quench tube adjacent one end of and coaxial with the resistance tube element, means disposed at the end of the graphite tube opposite the quench tube to substantial 1y prevent the egress of reaction gases formed in the apparatus during use, means to withdraw or allow removal of said reaction gases comprising a tubular member dis posed at a point removed from both ends of said substantially horizontal graphite tube, said graphite tube and said resistance element having apertures aligned with said tubular member to facilitate the Withdrawal or removal of said reaction gases.

An advantageous embodiment of the apparatus of the invention is illustrated in the drawings and includes a furnace comprising a substantially horizontal center tube 2 of graphite having a relatively thin wall and an internal diameter slightly greater than that of the cylinders 1. This tube is disposed axially of a graphite resistance element 3 in the form of a tube slit longitudinally (at 3a) from one end almost to the other end where it grips the adjacent end of the center tube 2 and also the inner end of a co-axially disposed graphite quench tube 4 spaced axially slightly from the center tube. Electric current is supplied to the element 3 by way of cables 5 and 6 respectively connecting terminal blocks 7 and 8 which are water-cooled and are each secured on one of the halves of the split end of the element, to the poles of a low voltage source of supply of electric current. These blocks are located outside a casing 9 within which the major part of the heating element 3 is received, it being disposed axially of a thermally insulating graphite tube 10 sup ported from the end walls of the casing. The front or outer end of the element 3 is supported from the thermal insulating tube lil'by means of an electrically insulating bushing 11 the temperature of which is kept within safe limits by a water-cooling system 12. On the front of the terminal blocks '7 and 8 is mounted, by means of an electrically insulating ring 13 and an insulating washer 14, a feed tube 15 which has an apertured rubber diaphragm 16 secured therein near its mouth, the circular aperture 16:: of this diaphragm being of a diameter somewhat smaller than that of a cylinder 1. Normally, one of these cylinders is left wedged in the aperture 16a, to constitute a gas seal, while another is being placed in position in the mouth of the feed tube, the pushing of the second cylinder into the aperture 16a displacing the first cylinder towards the tube 2. It will be understood that there would be, in practice, a continuous series of cylinders 1 (endtoen.d) extending from the diahpargm 16 to the discharge end of the quench tube 4.

In the upper part of the tube 2 is formed a gas outlet aperture 2a and at a corresponding location in theupper part of the tube it is formed a further gas outlet aperture in which is located a vertical gas outlet tube 17 of graphite, which may be attached to the tube 10 as shown in FIG. 2, surrounded by a graphite tube 13, the open upper end of this tube extending within a cylindrical neck 9a formed on the casing 9 and fitted with a cover 19 having an aperture 20 at which the gas evolved in the reaction may be burnt. Additional necks 9b are formed on the casing 9 to permit of the filling of the latter with a heat insulating material 21, such as carbon black, covers 22 being fitted over the mouths of these necks.

The quench tube 4 extends as a close fit through an outer copper tube 23 secured in a bush 24 serving to support the adjacent reduced diameter end lilo. of the tube 10 from the end wall of the housing and the outer tube 23 and bush 24 are intensively cooled by a circulation of water through a coiled copper tube 25. The outer flanged end of the outer tube 23 is secured to the adjacent and wall of a hood 2.6 which is furnished with a pressure-relief valve 27 and is firmly supported above a Water-filled tank 28 by arms (not shown) secured to the furnace. A 010- sure device (not shown) is mounted on the inner end of a rod 29 slidabie in a gas-tight manner through the hood wall so that it may be displaced to a position in which it seals the inlet into the hood, when desired. The open underside of the hood 26 has detachably secured thereto, by a gas-tight joint 30, a relatively large gas-tight canister 31 which depends into the body of water contained in the tank 28. The quench tube 4 projects a short distance within the hood 26 so that the cylinders 1a of titanium ca-nbide discharged from the tau-be may fiall into the can nister. The latter is removed and emptied from time to time, the inlet to the hood 26 being sealed by the closure device operated by the rod 29 before the cannister is removed and being unsealed again when the canister is back in position on the hood.

Aligned apertures 32 and 33 (see FIG. 3) are formed through the tube Ill and element 3 at the locations indicated in FIG. 1, sight tubes (not shown) being provided in register with these apertures and leading to the exterior of the housing 9 so that the temperature of the respective zones of the tube 2 may be determined when required. These tubes are sealed at their inner ends and open to atmosphere at their outer ends.

The gas outlet aperture 2a is located at a zone Where the temperature of the tube 2 is in the region of about 1500 to 2000" C., the gases evolved during the reaction passing out or" the tube 2 at that temperature to how through the slits 3a in the element 3-, and the annular space between the latter and the tube It to the outlet tube 17.

What I claim is:

1. An apparatus for the production of refnactory carbides, borides and the like comprising a furnace insulated from and disposed within an outer casing, 'sai-d furnace comprising a substantially horizontal graphite tube supported from end Walls of the casing and disposed axially within a graphite resistance element in the form of a longitudinally slit tube, a quench tube adjacent one end of and coaxial with said resistance element, means for supplying electric current to the resistance tube element, means disposed at the end of the :g-narphite tube opposite the quench tube to substantially prevent the egress of reaction gases formed in the apparatus during use, means for Withdrawing said reaction gases comprising a tubular member disposed at a point removed from both ends of said substantially horizontal graphite tube, said graphite tube and said resistance element having apertures aligned with said tubular member to facilitate the Withdrawal of said reaction gases.

2. An apparatus for the production of refinactory car: bides, borides and the like comprising a furnace insulated from and disposed within an outer casing, said furnace comprising a substantially horizontal graphite tu'be supported from end walls of the casing and disposed axially within a graphite resistance element, said graphite resist ance element comprising an elongated tube slit longitudinally from one end almost to the other end, said resistance element contacting the substantially horizontal graphite tube at the unslit end and maintained apart at the slit end by insulating means, a thermal insulating tube surrounding said resistance tube element and electrically insulated therefrom, a Water cooled quench tube adjacent and coaxial with the substantially horizontal graphite tube at the end which is in contact with the resistance tube element, means for supplying electric current to the resistance tube element, means disposed at the end of the substantially horizontal graphite tube to prevent the egress of reaction gases formed in the (apparatus during, use, outlet means for said reaction gases comprising a tubular member disposed at a point removed from both ends of said substantially horizontal graphite tube, said resistance heating tube and said substantially horizontal graphite tube having apertures aligned with said tubular member to facilitate the egress of said reaction gases.

3. An apparatus for the production of: refractory carbides, borides and the like comprising a furnace insulated from and disposed within an outer casing, said furnace comprising a substantially horizontal graphite tube supported Within the casing and disposed axially Within a graphite resistance element both of which extend through one outer casing end well, said graphite resistance element comprising an elongated tube slit longitudinally from one end almost to the other end, said resistance element contacting the substantially horizontal graphite tube at the unslit end Within the furnace and maintained apart at the slit end outside the casing by insulating means, a thermal insulating tube surrounding said resistance tube element and electrically insulated therefrom, a Water cooled quench tube adjacent and coaxial with the substantially horizontal graphite tube at the end which is in contact with the resistance tube element, means for supplying electric current to the resistance tube element, means disposed at the end of the substantially horizontal graphite tube to prevent the egress of reaction gases formed in the apparatus during use, outlet means for said reaction gases comprising a tubular member disposed at a point removed from both ends of said thermal insulating tube, said insulating tube, resistance heating tube, and substantially horizontal graphite tube having apertures aligned with said tubular member to facilitate the egress of said reaction gases.

References Cited in the file of this patent UNITED STATES PATENTS Amstein Jan. 30, 1962 

1. AN APPARATUS FOR THE PRODUCTION OF REFRACTORY CARBIDES, BORIDES AND THE LIKE COMPRISING A FURNACE INSULATED FROM AND DISPOSED WITHIN AN OUTER CASING, SAID FURNACE COMPRISING A SUBSTANTIALLY HORIZONTAL GRAPHITE TUBE SUPPORTED FROM END WALLS OF THE CASING AND DISPOSED AXIALLY WITHIN A GRAPHITE RESISTANCE ELEMENT IN THE FORM OF A LONGITUDINALLY SLIT TUBE, A QUENCH TUBE ADJACENT ONE END OF AND COAXIAL WITH SAID REISISTANCE ELEMENT, MEANS FOR SUPPLYING ELECTRIC CURRENT TO THE RESISTANCE TUBE ELEMENT, MEANS DISPOSED AT THE END OF THE GRAPHITE TUBE OPPOSITE THE QUENCH TUBE TO SUBSTANTIALLY PREVENT THE EGRESS OF REACTION GASES FORMED IN THE APPARATUS DURING USE, MEANS FOR WITHDRAWING SAID REACTION GASES COMPRISING A TUBULAR MEMBER DISPOSED AT A POINT REMOVED FROM BOTH ENDS OF SAID SUBSTANTIALLY HORIZONTAL GRAPHITE TUBE, SAID GRAPHITE 